What is undetectable?

Those currently living with HIV can reach undetectable levels by undergoing antiretroviral therapy. This means that they are much less likely to pass on the virus to others, many studies have estimated that the risk of passing on the virus with an undetectable viral load is greater to zero than any other figure if the antiretroviral therapy is adhered to for at least three months and then on-going afterwards. To put this more simply, if a HIV person were to sleep with somebody who is HIV negative and they have an undetectable viral load, the chances of contracting the virus are extremely minimal, either with anal or vaginal sex, with or without ejaculation.

What is a viral load?

The term viral load refers to the amount of HIV found in a blood sample, when your viral load is high, it determines you have a significant amount of HIV in your blood. Whilst taking antiretroviral therapy after three months, if your viral load test suggests that you have under 40-75 copies in a blood sample then these will be the levels needed in order to be deemed ‘undetectable’. The term ‘undetectable’ does not mean you are cured from the virus, however, your chances of passing on the virus are minimal and you will still need to continue your medication to remain healthy, whilst also at the same time reduce the risk of passing the virus on to potential sexual partners.

It is essential that you get a viral load test done once every 3-6 months and 2-8 weeks after either starting or changing your medication in order to see how the virus is responding.

Bare in mind that there is still a possibility that HIV can still exist in bodily fluids such as semen or vaginal fluids so it is still important to take precautionary measures in order to remain protected. Either condoms or please check out our section on where pre-exposure prophylaxis is available here.

Having another sexually transmitted disease in your bodily fluids can increase your viral load, therefore, increasing the risk of passing the virus on to other partners. This means that if you are living with HIV and also have another STD, you may be able to transmit HIV to your partner(s) even if your viral load is undetectable. This is another reason why it is important that you still get a regular viral load test for your own safety and also for others.


The most important part of being undetectable is to adhere to your medication, adherence has been proven to be extremely important and your chances of passing on the virus to somebody who is HIV negative is closer to nil than it is to 1%, however, this figure is only accurate if you adhere to your medication on a daily basis and that you make sure you attend regular appointments at your local sexual health clinic to test your viral load in order to make sure that your undetectable status still stands. In the event that you’re no longer undetectable, your sexual health adviser will more than likely put you on to a different course of medication that will hopefully react better to the virus.


Back in 2011 a study at The University of North Carolina enrolled 17,000 couples on to a trial who were all taking HIV meds, also known as ARV. Antiretroviral drugs are referred to as Combination ARV therapy (cART) is referred to as highly active ART(HAART). The issue we have with ART (antiretroviral therapy), is that it is estimated that there are 1.2 million people living with HIV in the US and only 37 percent of them are currently on antiretroviral drugs.

Out the 17,000 randomised couples who were taking part in the trial, there were only 4 cases of HIV being transmitted but it was concluded that the reason these four instances occurred was because the virus had not been suppressed yet by ART and they had not reached undetectable levels, this is exactly why adherence is very important and that HIV+ people are checked regularly.

Both the UK and US conclude that most patients on ART should be undetectable within a three month period, however, many become undetectable whilst on ART within one month. In some instances it can take longer depending if their viral load is very high when they start treatment.

Another study has also looked at HIV+ people with a viral load under 200 copies/ml and are yet to find a case where the virus has been transmitted to a HIV negative partner, to put it another way, a case has yet to be found where HIV has been transmitted either through anal or vaginal sex with a viral load under 200 copies/ml.

Under statistical analysis it has been said that the maximum likelihood of transmission was 1% per year for transmission through anal sex and 4% with anal sex through ejaculation, however it has been deemed that the true figure is closer to zero than 4% based on multiple studies. The 4% figure has taken in to account the included participants who have not yet been on ART long enough to be fully undetectable.

When asked what the study tells us about the chance of someone with an undetectable viral load  transmitting HIV, presenter Alison Rodger said: “Our best estimate is it’s zero.”

If you are a UK resident and feel like you might be HIV+ and would like more information on antiretroviral therapy please contact your nearest sexual health clinic. If you do not know where your nearest clinic is then please visit the NHS sexual health clinic finder here